Experimental study on the permeability of coal rocks of an gas-rich coal mine

Coal samples are collected from a Gas-rich Coal Mine. The micro-structure and porous characteristics of the samples are observed by using scanning electronic microscope. Electro-hydraulic servo tests of standard coal samples under complete stress-strain process are conducted by using the electro-hydraulic servo controlled rock mechanics testing system and the numerically controlled transient permeability method. Based on the experimental results, the Darcy flow permeability, non-Darcy flow permeability, non-Darcy flow factor β, and acceleration coefficient are calculated for different strains during the course of destruction of the coal samples. These relationship curves are obtained: principal stress difference vs. axial strain, permeability vs. axial strain, non-Darcy flow β factor vs. axial strain, and acceleration coefficient vs. axial strain. The study shows that the structure of the coal samples is homogeneous, consisting mainly of crustiform section, and radiate pinstripe structures, with some micro-porosity and micro-fissure being seen; that because of the action of peripheral pressure, during the course of destruction of coal samples, the permeability under complete stress-strain process changes as the strain increases, but does not change significantly; and that the non-Darcy flow factor β and acceleration coefficient have the same change tendency.